: The grid-marked maps in HOME are supposedly overlayable. Christopher Tolkien discusses this in one of the books, but I don't recall which one and am a little pressed for time right now.

: Basically, the Ered Luin chain was shortened (losing its southern peaks) and a gap was opened in the remaining mountans.

: Most of the land to the west of he Ered Luin sank into the sea (although it should more properly be said to have been destroyed by eruptions -- upheavals in the crust, great chasms opening due to the stresses put on the land by the Valar and Maiar, etc.).

: In the distant east the inland sea of Helcar was destroyed. I would guess that new lands rose up to compensate for the loss of land in the west. Presumably there would have been a lot of flooding. And all that remained (ultimately) of the inland sea was the little Sea of Rhun.

I've always felt that one of the little paleontological/geological things Tolkien put in there was the formation of lands between Mordor and Gondor. Looking at the map in LotR, it always seemed uncanny to me how the White Mountains and the Mountains of Mordor almost connected. And how the Anduin flowed right through. Given the time span discussed from the Silmarillion to LotR, I couldn't help thinking that a lot of erosion must have occured. Thinking that, I then noticed how right below Rauros, the Nindalf and the Dead Marshes spread out. I imagined how the Emyn Muil, the Ered Nimrais, and the Ered Lithui all formed something of a bowl.

To get the the point, I propose (to myself) that before the destruction of Beleriand, the Anduin flowed south into a great lake, perhaps even an arm of the great Inland Sea, and that the Anduin previously flowed around those volcanic (though dormant) mountains that became known as the Mountains of Ash, an arm of which became active again after many ages, culminating in the rising of Orodruin. When Beleriand was destroyed, Anduin broke through a new and wide pass in the mountains (several actually, creating the Isle of Cair Andros - where there are rapids, meaning the water is running quite swiftly, which could indicate that the Anduin flows downhill relatively rapidly right at that point, which could indicate that there was some altitude change at that point, before erosion flattened the whole thing out generally). That's my story, and I'm stickin' to it (until somebody points out a painfully obvious fact which would make this whole scenario impossible ;) ).

The point of this, is that I kind of think Tolkien did this deliberately.

So whaddaya think, eh?

Cheers.

Dave C-Q